CN102798512B - Three-dimensional flow field image measurement device and method adopting single lens - Google Patents

Abstract

The invention discloses a three-dimensional flow field image measurement device and method using a single lens. The characteristics are that a polarized light source is used to illuminate the flow field to be measured; For polarization analysis, two CCD or CMOS image sensors are used to image separately; from the relative gray scale of the corresponding tracer particles in the two pictures, it can be judged whether the tracer particles are located in front of the focal plane or behind the focal plane. Calculate the distance between the position of the tracer particle and the focal plane based on the defocus amount of the tracer particle, so as to uniquely determine the three-dimensional position of the tracer particle; combine the motion blur parameters to further obtain the three-dimensional motion velocity of the tracer particle, that is, obtain the information of the three-dimensional flow field The beneficial effect of the present invention is that only one camera lens can realize the three-dimensional measurement of the transient flow field, which simplifies the measurement system and data processing process and reduces the system cost.

Description

A three-dimensional flow field image measurement device and method using a single lens

technical field

The invention relates to an image measurement device and method for a three-dimensional flow field, in particular to a device and method for acquiring three-dimensional flow field information based on fuzzy image processing and using a single lens.

Background technique

In recent years, with the development of digital cameras and computer technology, flow field measuring instruments that use digital cameras to capture trace particles to obtain flow field information have been widely used. For the acquisition of three-dimensional flow field information, two or more sets of shooting systems are usually used to perform imaging from two or more perspectives. There are synchronization problems between two or more sets of shooting systems, the adjustment is very difficult, and the data processing is complicated; and in order to shoot clear particle transient images or interference images, the exposure time is usually required to be extremely short, and high-speed cameras and High-energy pulsed laser light source, etc., the system cost is high.

Contents of the invention

The purpose of the present invention is to develop a device and method based on fuzzy image processing and using a single lens to measure a three-dimensional flow field, which has the advantages of simple device, easy operation and low cost.

The basic principle of the present invention: in the flow field measurement process commonly used at present, on the one hand, in order to avoid the image quality degradation caused by the movement of the tracer particles, the exposure time is required to be extremely short; but from another point of view, if appropriate Prolonging the exposure time, the motion of the tracer particles within this time will form a blurred trajectory image, which contains the motion information of the tracer particles, that is, the velocity field information. On the other hand, in order to prevent defocus blur from interfering with the measurement results, conventional measurement methods use a thin laser sheet light source to illuminate the area within the depth of field, so that the illuminated tracer particles can be clearly displayed on the focal plane of the camera However, from another point of view, the defocusing phenomenon of the image actually contains the information of the distance between the tracer particles and the focus plane, and further determines whether the tracer particles are located in front of or behind the focus plane, combined with the plane of the two-dimensional image coordinates, the accurate three-dimensional position information of the tracer particles can be obtained. By combining the above two points, accurate three-dimensional flow field information can be obtained.

Based on the above-mentioned invention principle, the technical solution of the present invention is: a three-dimensional flow field image measurement device using a single lens, which is characterized in that the device consists of a polarized light source, a lens, a beam splitter, a first polarizer, a second polarizer, The first image sensor, the second image sensor and a computer are composed, the polarized light source is placed on the flow field to be measured or illuminates the flow field to be measured through a window, the beam splitting prism is placed behind the lens, and the incident surface of the beam splitting prism A is opposite to the lens, the first image sensor and the second image sensor are respectively arranged at equal optical path distances on one side of the beam splitting prism exit surface B and the exit surface C, and the first polarizer and the second polarizer are respectively arranged on the beam splitter Between the second exit surface C of the prism and the first image sensor, between the first exit surface B of the dichroic prism and the second image sensor. The dichroic prism can be a half-transparent and half-reflective prism, a pentagonal dichroic prism or other types of dichroic prisms.

The first polarizer and the second polarizer can be coated on the two surfaces of the first exit surface B and the second exit surface C of the dichroic prism to form a whole, or the dichroic prism, the first polarizer and the second polarizer The plate is replaced by a polarizing beamsplitter.

The beam-splitting prism can be replaced by a semi-transparent and semi-reflective plane beam-splitter.

The lens is a telecentric lens or a non-telecentric lens, and the first image sensor and the second image sensor are CCD or CMOS devices.

A three-dimensional flow field image measurement method using the above-mentioned single-lens three-dimensional flow field image measurement device, characterized in that the steps of the measurement method are:

1. Before measurement, first calibrate the measurement device with a transparent calibration object to obtain the actual size represented by the pixel (pixel);

2. Use a polarized light source to illuminate the flow field to be measured, adjust the position and intensity of the polarized light source, and adjust the polarization angle to make the background light uniform;

3. The beam-splitting prism is placed behind the lens, and the beam-splitting prism divides the received light source into two paths. After the two paths of light are analyzed by the first polarizer and the second polarizer whose polarization angles are perpendicular to each other, CCD or The imaging of the first image sensor and the second image sensor of CMOS, because the optical path distance between the two image sensors and the lens is the same, that is to ensure that the captured field of view is exactly the same;

4. Adjust the exposure time of the camera to reduce the coincidence and adhesion of tracer particle trajectories in the image sensor imaging, and take pictures of the tracer particles in the area of the flow field to be measured, and input the acquired images into the computer;

5. On the computer, denoise the collected images first, and then judge the defocusing amount of the image through the gradient change of the blurred edge scale of the image. Considering that the fields of view of the two images corresponding to different polarization directions are exactly the same, the two images The relative grayscale of the corresponding tracer particles in the picture can determine whether the tracer particles are located in front of the focus plane or behind the focus plane, so as to establish the corresponding relationship between the blur scale δ and the defocus amount ΔW , as shown in formula 1,

(1)

In the formula, R' is the blurred image radius of out-of-focus particles, ΔW is the distance from the actual object plane to the focus plane, W obtained from the camera parameters is the object distance when the focus is accurate, and δ is the blurred image radius R' of out-of-focus particles The difference between the particle radius and the particle radius calculated from the maximum magnitude of the two edge gradients in the radial direction of the blurred image; the gradient magnitude of the blurred image can be calculated from the following formula:

(2)

where f(x,y) is the coordinate function of the tracer particle image pixel;

Since the fields of view of the two pictures corresponding to different polarization directions are exactly the same, the relative gray scale of the corresponding tracer particles in the two pictures can be used to determine whether the tracer particles are located in front of the focal plane or behind the focal plane, and thus the tracer particle can be uniquely determined. The three-dimensional position of the particle; during the exposure time, when the particle has a displacement along the direction perpendicular to the camera plane, the above method can be used to judge the change of the defocus amount along the motion direction, and combined with the length of the particle motion blur track on the imaging plane, the three-dimensional motion direction of the particle can be obtained and the actual trajectory length L , and the camera exposure time t is known, the three-dimensional velocity V of the tracer particles can be obtained by the following formula:

(3)

In this way, the three-dimensional flow field information is obtained through the processing of the blurred image.

The beneficial effect of the present invention is that only one lens can be used to realize the three-dimensional measurement of the flow field, instead of two or more cameras shooting the tracer particles of the flow field to be measured from different angles, or one camera moving quickly to take pictures of the flow field to be measured The tracer particles in the flow field not only avoids the synchronization problem of two or more systems, but also simplifies the measurement system and data processing process, and reduces the system cost.

Description of drawings

Fig. 1 is the schematic diagram of embodiment 1 of the present invention;

Fig. 2 is the schematic diagram of Embodiment 2 of the present invention;

Fig. 3 is a schematic diagram of Embodiment 3 of the present invention.

Fig. 4 is the schematic diagram of Embodiment 4 of the present invention;

Fig. 5 is a schematic diagram of Embodiment 5 of the present invention.

Detailed ways

Embodiment 1 of a three-dimensional flow field image measurement device using a single lens, as shown in Figure 1, is characterized in that the device consists of a polarized light source 1, a lens 2, a beam splitting prism 3, a first polarizer 4, and a second polarizer 5 , a first image sensor 6, a second image sensor 7 and a computer 8, the polarized light source 1 is placed on the flow field to be measured to illuminate the flow field through a window, the beam splitter 3 is placed behind the lens 2, and the beam splitter The incident surface A of the prism 3 is opposite to the lens 2, and the second image sensor 6 and the first image sensor 7 arranged at equal optical path distances on one side of the first exit surface B and the second exit surface C of the dichroic prism 3 respectively, the described The first polarizer 4 and the second polarizer 5 are respectively arranged between the second exit surface C of the dichroic prism 3 and the first image sensor 6 , and between the first exit surface B of the dichroic prism 3 and the second image sensor 7 .

The steps of a three-dimensional flow field image measurement method using the above-mentioned single-lens three-dimensional flow field image measurement device are:

1. Before the measurement, first calibrate the measurement device; take a transparent calibration object such as a microscale as the measurement object, and obtain the actual size represented by the unit pixel of the image sensor 6 and 7 under the measurement focal length;

2. Use polarized light source 1 to illuminate the flow field to be measured, adjust the position and intensity of polarized light source 1, and adjust the polarization angle to make the background light uniform;

3. After the beam-splitting prism 3 is placed behind the lens 2, the beam-splitting prism 3 divides the received light source into two paths. The first image sensor 6 and the second image sensor 7 of CCD or CMOS are used for imaging, since the optical path distances of the two image sensors and the lens 2 are the same, that is, the field of view captured is guaranteed to be exactly the same;

4. Adjust the exposure time of the camera to reduce the coincidence and adhesion of tracer particle trajectories in the image sensor imaging, and take pictures of the tracer particles in the flow field area to be measured, and input the acquired images into the computer;

5. On the computer 8, denoising is first performed on the collected images, and then the defocusing amount of the image is judged by the gradient change of the blurred edge scale of the image. Considering that the fields of view of the two pictures corresponding to different polarization directions are exactly the same, the two pictures The relative grayscale of the corresponding tracer particles in can determine whether the tracer particles are located in front of the focal plane or behind the focal plane, so as to establish the corresponding relationship between the blur scale δ and the defocus amount ΔW, as shown in formula 1,

(1)

In the formula, R' is the blurred image radius of out-of-focus particles, ΔW is the distance from the actual object plane to the focus plane, W obtained from the camera parameters is the object distance when the focus is accurate, and δ is the blurred image radius R' of out-of-focus particles The difference between the particle radius and the particle radius calculated by the maximum magnitude of the two edge gradients in the radial direction of the blurred image;

The gradient magnitude of the blurred image can be calculated from the following formula:

(2)

where f(x,y) is the coordinate function of the tracer particle image pixel;

Since the fields of view of the two pictures corresponding to different polarization directions are exactly the same, the relative gray scale of the corresponding tracer particles in the two pictures can be used to determine whether the tracer particles are located in front of the focal plane or behind the focal plane, and thus the tracer particle can be uniquely determined. The three-dimensional position of the particle; during the exposure time, when the particle has a displacement along the direction perpendicular to the camera plane, the above method can be used to judge the change of the defocus amount along the motion direction, and combined with the length of the particle motion blur track on the imaging plane, the three-dimensional motion direction of the particle can be obtained and the actual trajectory length L , and the camera exposure time t is known, the three-dimensional velocity V of the tracer particles can be obtained by the following formula:

(3)

In this way, the three-dimensional flow field information is obtained through the processing of the blurred image.

Example 2:

As the first polarizer 4 and the second polarizer 5 in embodiment 1 are plated on two surfaces of the second exit surface C of the dichroic prism and the first exit surface B in the form of coating, as shown in Figure 2, the embodiment The dichroic prism 3, the first polarizer 4 and the second polarizer 5 in 1 form a whole, and the measurement steps are the same as the operation process of the embodiment 1.

Example 3:

As shown in Figure 3, the dichroic prism 3, the first polarizer 4 and the second polarizer 5 in the embodiment 1 can also be replaced by the polarization beam splitter prism 9, and the first image sensor 6 and the second image sensor 7 are then equal to The optical path distances are respectively placed on the sides of the two outgoing surfaces of the polarizing beam splitter prism 9 , and the measurement steps are the same as those in Embodiment 1.

Example 4:

As shown in Fig. 4, also can replace beam splitting prism 3 among the embodiment 1 with plane beam splitter 10, this plane beam splitter 10 is to coat beam splitting film formation on the optical flat plate.

Example 5:

As shown in FIG. 5 , the lens 2 adopts the telecentric lens 11 , and within the depth of field of the telecentric lens, the image size of the object does not change with the position, so that the size of the tracer particles or other particles can be obtained. The measurement steps are also the same as in Example 1.

In the above five embodiments, both the first image sensor and the second image sensor use CCD or CMOS devices. In the above-mentioned embodiments 1, 2, 3, and 4, the lens 2 is a non-telecentric lens. In embodiment 5, the lens 2 is a telecentric lens, and the lens number 2 is changed to 11.

Claims (1)

1. A three-dimensional flow field image measurement method using a single-lens three-dimensional flow field image measurement device, the device consists of a polarized light source (1), a lens (2), a beamsplitter prism (3), and a first polarizer (4) , a second polarizer (5), a first image sensor (6), a second image sensor (7) and a computer (8), the polarized light source (1) is placed on the flow field to be measured, and the light splitter The prism (3) is placed behind the lens (2), the incident surface A of the beam splitting prism (3) is opposite to the lens (2), and the second exit surface C and the first exit surface B of the beam splitting prism (3) are respectively The first image sensor (6) and the second image sensor (7) are set at the same optical path distance, and the first polarizer (4) and the second polarizer (5) are respectively arranged at the second exit of the beam splitter (3) The middle between the surface C and the first image sensor (6) and the first exit surface B of the dichroic prism (3) and the middle of the second image sensor (7); it is characterized in that the steps of the measurement method are: 1) Before the measurement, first calibrate the measuring device, and use a transparent calibration object to obtain the actual size represented by the pixel; 2) Use the polarized light source (1) to illuminate the flow field to be measured, adjust the position and intensity of the polarized light source (1), and adjust the polarization angle to make the background light uniform; 3) After the beam splitting prism (3) is placed behind the lens (2), the beam splitting prism (3) divides the received light into two paths, and uses the first polarizer (4) and the second polarizer whose polarization angles are perpendicular to each other for the two paths of light. After the two polarizers (5) are analyzed, the first image sensor (6) and the second image sensor (7) of CCD or CMOS are respectively used for imaging. Since the optical distance between the two image sensors and the lens (2) is the same, That is to ensure that the captured field of view is exactly the same; 4) Adjust the exposure time of the camera to reduce the trace overlap and adhesion of the tracer particles in the imaging of the image sensor, take pictures of the tracer particles in the flow field area to be measured, and input the acquired images into the computer (8); 5) On the computer (8), denoise the collected images first, and then judge the defocus amount of the image through the gradient change of the image blur edge scale. Considering that the fields of view of the two images corresponding to different polarization directions are exactly the same, from this The relative gray scale of the corresponding tracer particles in the two pictures can determine whether the tracer particles are located in front of the focal plane or behind the focal plane, so as to establish the corresponding relationship between the blur scale δ and the defocus amount ΔW, as shown in formula 1, (1) In the formula, R' is the blurred image radius of out-of-focus particles, ΔW is the distance from the actual object plane to the focus plane, W obtained from the camera parameters is the object distance when the focus is accurate, and δ is the blurred image radius R' of out-of-focus particles The difference between the particle radius and the particle radius calculated by the maximum magnitude of the two edge gradients in the radial direction of the blurred image; The gradient magnitude of the blurred image can be calculated from the following formula: (2) where f(x,y) is the coordinate function of the tracer particle image pixel; Since the fields of view of the two pictures corresponding to different polarization directions are exactly the same, the relative gray scale of the corresponding tracer particles in the two pictures can be used to determine whether the tracer particles are located in front of the focal plane or behind the focal plane, and thus the tracer particle can be uniquely determined. The three-dimensional position of the particle; during the exposure time, when the particle has a displacement along the direction perpendicular to the camera plane, the above method can be used to judge the change of the defocus amount along the motion direction, and combined with the length of the particle motion blur track on the imaging plane, the three-dimensional motion direction of the particle can be obtained and the actual trajectory length L , and the camera exposure time t is known, the three-dimensional velocity V of the tracer particles can be obtained by the following formula: (3) In this way, the three-dimensional flow field information is obtained through the processing of the blurred image.